Catheters for insertion and deployment within blood vessels and cardiac chambers are well-known in the art. A variety of catheters are now utilized in the diagnosis and treatment of cardiac disease. Among the ensemble of catheters used in cardiac care are ultrasound imaging catheters which can be inserted within the heart (i.e., intracardial) to obtain two-dimensional ultrasound images of heart structures and measure blood flow. Such intracardial echocardiography (ICE) catheters provide cardiologist and heart surgeons with unique viewing perspectives beneficial to diagnosis and treatment of heart diseases.
To obtain diagnostically useful images, an ultrasound imaging catheter can be positioned next to or within the vessels and chambers of the heart. Typically, the catheter is introduced into a patient through the femoral, subclavian or jugular veins and maneuvered into the right atrium. From there an ultrasound imaging catheter can image the heart anatomy including both left and right atriums, ventricles, the valves, and the atrial and ventricular septal walls. The catheter can also be advanced through the tricuspid valve into the right ventricle from which the right and left ventricles, the septum, the valves and the left atrium may be imaged.
Traditionally there have been two basic methods for positioning ultrasound imaging catheters within the chambers of the heart. In the first method a guide wire is threaded through the patient's vascular structure via catheterization and under fluoroscopy until the distal end reaches a proper position for imaging. A sheath is then extended over the guide wire. Finally, the guide wire is withdrawn and the ultrasound imaging catheter inserted into the sheath. Held in relative position by the sheath, the imaging catheter can be advanced to penetrate deeper into the heart or rotated in order to scan of the heart.
The second method uses a steerable ultrasound imaging catheter to maneuver the catheter into position without the use of a guide wire. An example of a steerable ultrasound imaging catheter 1 is provided in FIGS. 1 and 2. Such steerable catheters 1 included a bendable portion 9 near the ultrasound transducer assembly 4 at the distal end of an elongated catheter body 2. Steering is achieved by tensioning a steering cable attached at or near the distal portion and running down the interior of the catheter to a wheel or knob in the handle 7. When the steering cable is tensioned while the catheter shaft is restrained, the tip will deflect resulting in a bend near the distal end of the catheter as illustrated in FIG. 2. Alternatively, the steering cable may be restrained while the shaft portion 2 is advanced distally, producing the same effect. Typically the induced bend has a radius of curvature of about four inches within an arch defining a plane of fixed orientation with respect to the catheter body 2 and handle 7. The catheter shaft (2) can also be rotated clockwise or counterclockwise to direct the ultrasound transducer face in the desired direction. By rotating the catheter shaft and bending the distal curve 9 the transducer face can be directed as needed. Electrical/signal coaxial cables to/from the ultrasound transducer assembly 4 pass through the catheter body 2 and through the handle 7 to exit as a cable 8 for connection to ultrasound imaging equipment. By being able to bend the distal portion 9 of the catheter, the catheter body 2 can be maneuvered through the patient's vein and into heart chambers without the need for the extra time and steps required by the guide wire and sheath catheterization method.
While the steerable ultrasound catheter obviates the need for a sheath and guide wire, the viewing angle of the ultrasound imaging catheter is restricted due to the bend 9 in the catheter that must be made to properly position the ultrasound imaging assembly 4 within a heart chamber. Rotating the catheter shaft by rotating the handle would cause the ultrasound imaging assembly 4 to swing about. As the transducer face is linear and parallel to the catheter shaft, and because the two directional controls are limited, the, current design steerable ultrasound catheters provide a limited three-dimensional viewing perspective.